the first thing i would do is to change msgstr of translatable string and see if the changes are visible to the code.

also, what is strange is that msgctxt is non-empty, while to get translation i18n is used and not i18nc.

> msgctxt "action"
> msgid "Save Incremental &Version"
> msgstr "増分バージョンを保存(&V)"
...
> return i18n(s.toUtf8().constData());

also toLatin1() would be enough, i believe.
and even better is to pass msgid content as qbytearray or const char* everywhere